Regarding slow initial PHPStorm startup in Windows (date: 10/03/2019):
Could I suggest the solution is added to Windows install readme file or something readily available as it makes a big difference to user experience.
Splash screen takes 20-30 seconds to even load... making you think you haven't double-clicked the program properly and sometimes do it again!
Total program load time: 45 seconds.
Subsequent restarts are much faster (10-15 secs)
Add the JetBrains folder to Defender exclusions
Now, PHPStorm loads in 15 seconds from a fresh boot which is perfectly acceptable.
New Windows 10 install with Lenovo P50 32GB